The evaluation of the nutrient composition of feeds and foods has traditionally included an analysis of crude fat. Crude fat is primarily a measure of the triglyceride content of the food or feed and represents the more energy dense component. Fat is commonly extracted from feed and food with diethyl either or petroleum ether. Compounds other than fat are soluble in diethyl ether or petroleum ether but they represent minor components in relation to the energy contribution to the diet and generally fall in the category of lipids. The quantitative analysis of crude fat has traditionally been accomplished by the Soxhlet extraction technique (Quantitative Chemical Analysis, by Hamilton and Simpson). The current state of the art of fat analysis is described in, xe2x80x9cMethods of Analysis for Nutritional Labelingxe2x80x9d. The standardized Soxhlet technique is detailed by the Association of Official Analytical Chemists in the AOAC Official Method 920.39. This Soxhlet technique involves placing an individual sample in a filter chamber. This filter chamber is then placed in the siphoning compartment. The heater boils the solvent, commonly petroleum ether, and passes the vapor into a condenser. The condenser condenses the vapor into a liquid, channels it into the filter chamber and siphoning compartment. The solvent is periodically siphoned back into the distilling flask after it reaches a certain level in the siphoning compartment. The distillation/extraction process is continued for four to sixteen hours. The fat content of the sample is then determined either by evaporating the solvent and measuring the remaining fat directly or indirectly by weighting the weight loss of the sample contained in the filter chamber. The filter chambers that are commonly used are thimble shaped filter paper. Glass filter chambers with fritted glass filters and fritted Alundum thimbles are also used.
As described above, the prior art for crude fat analysis that is currently being used by regulatory laboratories, industry and academia involves individual analysis based on the traditional Soxhlet technique.
Apparatus designed to expedite the Soxhlet extraction process and improve the manual efficiency of the extraction process are described in U.S. Pat. No. 4,184,961. Improvements in the rate of extraction and solvent penetration of the sample matrix have been achieved by increasing the temperature and pressure of the extracting solvent as taught by U.S. Pat. No. 4,265,860. These instruments have the same limitation as the standard Soxhlet process of dealing with individual samples individually throughout the analysis. These instruments deal with individual samples in multiple setups and semi-automate or automate individual steps such as extraction, rinsing and solvent evaporation. These instruments can only process a limited number of samples since they deal with samples individually (up to twelve), and require costly equipment when calculated on a per sample basis.
In all of the systems described above, the samples are processed individually in order to yield a unique value for each sample. This requirement of individual sample processing limits the efficiency of the analysis and increases the cost of the instrument by requiring a replicate of the apparatus for each sample capable of being analyzed by the instrument.
U.S. Pat. 5,370,007 is directed to a Fiber Analysis System in which a sample of a feedstuff or food of a predetermined weight is sealed in a filter bag with selected porosity which recovers the fiber components while allowing the removal of the detergent soluble components of the sample. The fiber analysis taught by the ""007 patent is accomplished by exposing the sample to an aqueous detergent solution (polar solvent) under heated conditions for a time sufficient to remove substantially all soluble solids from the feed while retaining the fiber components within the filter bag. The preparation of samples for analysis requires that the samples be ground to a fine particle size in order to ensure a representative aliquot. The sample grinding process fractures and fragments the different components of the feed differently. Non-fiber components such as non-structural carbohydrates, sugars, proteins, and minerals fracture into much finer particles than the fiber components. Because the large majority of fine particles are not fiber, their passage through the fiber filter media causes no error. Therefore the filtration media used in these filter bags benefits from the surface tension of the aqueous solution, and from the fact that very fine particles are soluble and do not need to be retained. To ensure accurate fiber results, only retention of particles larger than 25 microns is required for the filter media.
The significant differences between fiber analysis of the prior art and fat analysis of the present invention include: retention vs extraction of the analyte; the use of aqueous solutions vs. organic solvents; and the retention of coarse particle vs fine particle; 25 micron vs  less than 4 micron filter media. These differences will become more apparent with a reading of the detailed description of the invention.
It is therefore an object of the present invention to provide a method of determining crude fat content of a feedstuff or food which overcomes the problems of the prior art described above.
It is another objective of the present invention to provide an efficient system for simultaneously determining the fat content of individual samples.
It is another object of the present invention to provide a system for determining the fat content of a food or feed by a novel batch processing system.
It is a further object of the present invention to improve the efficiency of performing a fat extraction.
It is also an objective of this invention to reduce the cost of the analysis and increase the capacity of a fat extraction instrument.
It is yet another objective to provide a system for processing samples in a batch which enables one instrument to perform numerous extractions simultaneously.
It is another object of the present invention to provide an effective filtering chamber that will retain very fine particles, and still provide adequate access to the exchange of solvent.
It is yet another object of the present invention to provide for a pretreatment of samples in batch to break down the bound fat to improve the efficiency of the fat analysis.
It is a further object of the present invention to provide for a pretreatment which results in a more efficient determination of the total fat content of a sample.
The present invention is based on the discovery that crude fat content of individual samples can be determined, in batch, by encapsulating a quantitative aliquot of each sample in the filter media and simultaneously extracting the crude fat with a suitable solvent under controlled conditions of temperature and pressure. Suitable solvents for crude fat analysis include either diethyl ether or petroleum ether. The crude fat content can then be determined by the loss in weight of the samples after rinsing and drying the sample. Other solvents, used in the determination of fat and lipids, such as methylene chloride, and mixtures of chloroform/methanol and diethyl ether/ethanol can also be used in this invention. The filter media for other prior art techniques was not capable of performing this analysis. The success of this system of analysis using the batch process required the development of unique filter media with the capability of retaining 4 micron size and larger particles while permitting sufficient flow of the solvent to efficiently extract all the crude fat. The main advantage of the present invention over the conventional prior art is that it greatly improves the efficiency of the analysis. A technician can analyze twenty samples simultaneously, processing 200 or more samples a day. The invention further includes a pretreatment by exposing the samples in batch to a strong acid or base which functions to break down the bonds which bind the fat to the sample matrix. This pretreatment results in more efficient release of fat from samples and enables the analysis of bound and unbound fat.